This invention relates generally to the field of heat pumps, and more particularly to a fixed-speed duct-free split heat pump unit.
Heat pump systems use a refrigerant to carry thermal energy between a relatively hotter side of a circulation loop to a relatively cooler side of the circulation loop. Compression of the refrigerant occurs at the hotter side of the loop, where a compressor raises the temperature of the refrigerant. Evaporation of the refrigerant occurs at the cooler side of the loop, where the refrigerant is allowed to expand, thus resulting in a temperature drop. Thermal energy is added to the refrigerant on one side of the loop and extracted from the refrigerant on the other side, due to the temperature differences between the refrigerant and the indoor and outdoor mediums, respectively, to make use of the outdoor mediums as either a thermal energy source or a thermal energy sink. In the case of an air to water heat pump, outdoor air is used as a thermal energy source while water is used as a thermal energy sink.
The process is reversible, so the heat pump can be used for either heating or cooling. Residential heating and cooling units are bidirectional, in that suitable valve and control arrangements selectively direct the refrigerant through indoor and outdoor heat exchangers so that the indoor heat exchanger is on the hot side of the refrigerant circulation loop for heating and on the cool side for cooling. A circulation fan passes indoor air over the indoor heat exchanger and through ducts leading to the indoor space. Return ducts extract air from the indoor space and bring the air back to the indoor heat exchanger. A fan likewise passes ambient air over the outdoor heat exchanger, and releases heat into the open air, or extracts available heat therefrom.
These types of heat pump systems operate only if there is an adequate temperature difference between the refrigerant and the air at the respective heat exchanger to maintain a transfer of thermal energy. For heating, the heat pump system is efficient provided the temperature difference between the air and the refrigerant is such that the available thermal energy is greater than the electrical energy needed to operate the compressor and the respective fans. For cooling, the temperature difference between the air and the refrigerant generally is sufficient, even on hot days.
Under certain operating conditions, frost builds up on a coil of the heat pump. The speed of the frost build-up is strongly dependent on the ambient temperature and the humidity ratio. Coil frosting results in lower coil efficiency while affecting the overall performance (heating capacity and coefficient of performance (COP)) of the unit. From time to time, the coil must be defrosted to improve the unit efficiency. In most cases, coil defrosting is achieved through refrigerant cycle inversion. The time during which the coil defrosting occurs impacts the overall efficiency of the unit, since the hot refrigerant in the unit, which provides the desired heat, is actually cooled during coil defrosting.
In a fixed-speed duct-free split heat pump unit that doesn""t have an electronic control device board on the outdoor unit, the defrost operation which eliminates the frost accumulated on the outdoor heat exchanger during heating operation requires feedback from the outdoor unit to the indoor unit to terminate the defrost operation.
Referring to FIG. 1, in the prior art of defrost termination detection feedback, a low voltage sensor 10 is needed for the outdoor heat exchanger temperature detection. This requires two low voltage lines of interconnection wires 14, 16 to connect sensor 10 to an indoor electronic control 12.
Referring to FIG. 2, when a high voltage thermostat 18 is used to detect the outdoor heat exchanger temperature, an additional high voltage interconnection wire 20 is needed for the feedback to indoor electronic control 12.
Referring to FIG. 3, a system which uses an outdoor sensorless defrost algorithm includes a current transformer 22 on indoor electronic control 12 to measure current flows through a compressor 24 to detect the defrost termination point. When the heat pump unit is too large to use a power relay on indoor electronic control 12, a magnetic contactor 26 is used to turn compressor 24 on and off. There is then a need for an additional high voltage interconnection wire 28 to make the compressor current flow through the current transformer loop on indoor electronic control 12.
Briefly stated, a heat pump system includes an indoor unit and an outdoor unit, with a compressor, an outdoor fan, and a reversing valve all in the outdoor unit. A thermostat is added to the outdoor unit with one side of the thermostat connected to a high voltage line for either a compressor or a magnetic contactor and the other side connected to a high voltage line for either an outdoor fan or a reversing valve. A signal collection circuit in the indoor unit is connected to a high voltage line for the outdoor fan when the other side of the thermostat is connected to the outdoor fan and to a high voltage line for the reversing valve when the other side of the thermostat is connected to the reversing valve. The thermostat sends a signal to the electronic control board when the defrosting operation should be terminated.
According to an embodiment of the invention, a heat pump system includes an indoor unit and an outdoor unit, along with a compressor, an outdoor fan, and a reversing valve all in the outdoor unit; a thermostat in the outdoor unit; a first side of the thermostat connected to a high voltage line for one of a compressor and a magnetic contactor and a second side of the thermostat connected to a high voltage line for one of an outdoor fan and a reversing valve; and a signal collection circuit in the indoor unit connected to a high voltage line for the outdoor fan when the second side of the thermostat is connected to the outdoor fan and to a high voltage line for the reversing valve when the second side of the thermostat is connected to the reversing valve.
According to an embodiment of the invention, a method for terminating a defrost operation in a heat pump system having an indoor unit and an outdoor unit includes the steps of connecting, in the outdoor unit, a first side of a thermostat between a high voltage line for one of a compressor and a magnetic contactor and connecting a second side of the thermostat to a high voltage line for one of an outdoor fan and a reversing valve; connecting, in the indoor unit, a signal collection circuit to a high voltage line for the outdoor fan when the second side of the thermostat is connected to the outdoor fan, and to a high voltage line for the reversing valve when the second side of the thermostat is connected to the reversing valve; and terminating the defrost operation when the thermostat is activated upon reaching a predetermined temperature.